Unless he or she actually lives there, there is one, and only one, reason for a politician to visit a disaster area. That reason is to be seen visiting a disaster area.
And every time a politician visits a disaster area, that politician and his or her security/campaign/personal entourage, plus whatever media crews show up for the visit (but didn't show up for the disaster) are hogging up valuable resources (plane seats that could be bringing actual emergency workers in, bottles of water that people who belong there could be drinking, etc.).
He or she is also causing local police, emergency workers, etc. to stop working on actual disaster relief stuff and waste their time escorting his or her dumb ass around while cameras shoot video of everyone gesticulating wildly as if they're conferring on important things.
I won't say it's a litmus test, exactly, but whenever I see a politician pulling that kind of crap, I make a little mark in my brain on the "don't vote for this grandstanding idiot" side of the ledger. Just sayin'.